Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
A typical image forming apparatus, such as a printer-only machine and a Multifunction Peripheral (MFP), has input-output characteristics that changes due to a cause such as a secular change of a print device. For example, there is known the following two methods as calibration methods performing a correction of the input/output characteristics, so-called gamma correction.
The first method forms a plurality of color patches on an image carrier on which a toner image is to be formed, and then detects color values of the patches formed on the image carrier with a sensor, so as to correct the input-output characteristics based on the detected color values.
The second method prints a plurality of color patches on a recording medium such as a paper sheet, then reads color values of the patches printed on the recording medium with a reading device such as a scanner, and detects the color values of the patches in an image read and generated by the reading device, so as to correct the input-output characteristics based on the detected color values.
Comparing the above-described two methods, the second method detects the color values of the patches actually printed on the recording medium. Compared with the first method, the second method ensures highly-accurate calibration.
However, with an image forming apparatus that does not include the reading device, such as the scanner, such as the printer-only machine, since the image forming apparatus does not include the reading device, the image forming apparatus cannot perform the second method. Therefore, the image forming apparatus needs to perform the calibration by the first method.
Therefore, there has been proposed a new method that does not read the patches printed on the recording medium by the reading device such as the scanner, records the patches by an imaging device, such as a digital camera, located outside of the image forming apparatus, and then detects color values of the patches in an image taken and generated by the imaging device, so as to correct the input-output characteristics based on the detected color values.
A typical calibration method first simultaneously takes a reference sheet and a test sheet with the imaging device. On the reference sheet, a reference chart that includes a plurality of color patches is drawn. On the test sheet, a test chart that includes a plurality of color patches is printed with the print device of the image forming apparatus. Based on an RGB value of each patch of the reference chart and the test chart in the image taken and generated by the imaging device, tone characteristics of the print device are corrected.
Another typical calibration method first separately takes a reference sheet and a test sheet with the imaging device. On the reference sheet, a reference chart that includes a plurality of color patches is drawn. On the test sheet, a test chart that includes a plurality of color patches is printed with the print device of the image forming apparatus. Subsequently, based on color values of patches of the reference chart in the first image taken and generated by the imaging device and color values of patches of the test chart in the second image taken and generated by the imaging device, a first correction value is calculated. Based on the color values of the patches in the reference chart in the first image taken and generated by the imaging device and reference color values preliminary stored in an image forming apparatus, a second correction value is calculated. Then, based on the first correction value and the second correction value, tone characteristics of the print device are corrected.